Some speculation, as I'm working through White Eagle, Red Star.
August, 1920
The people of Warsaw stared sullenly at the men of the Red Army as they advanced through the streets of their city. Yet while they were frowning, General Tukhachevsky of the Red Army smiled. “And you thought we could lose,” he said to Trotsky, who sat in the car next to him.
Trotsky scowled. “I did not think we would lose,” he replied. “History assures our triumph. What I said that the Revolution would come from within, as the Polish workers and peasants rose up.”
“They did,” replied Tukhachevsky. “There were plenty of Poles serving in the Red Army.” He left unspoken the fact that he was one such. “And so the Red Army helped the Revolution along.”
Trotsky leaned back in the car and sighed. “Well enough,” he said. He thought for a moment, and said, “What do you think of Lithuania?” he asked.
Tukhachevsky shrugged. “Why bother?” he asked. “They gave us passage through Vilnus to attack Poland. Estonia’s already signed a treaty with us, and Latvia is,” he shrugged, “Latvia. They’ll fold in time.” [1]
Trotsky frowned. “The Soviet Union needs an ice free port,” he pointed out.
Tukhachevsky began laughing. “What for, Comrade? We don’t have a navy. We won’t have one any time soon. The Soviet Union is a peaceful nation, after all.”
Tukhachevsky paused, frowning as he saw the looks on the faces of his countrymen. “Besides,” he said, “We will need our army here.”
The Birth of the Polish Soviet Republic
While Warsaw fell by August 17, Poland still had numerous forces in the field. It is therefore worth asking why Poland’s forces were not able to rally in Poznan and defeat the Soviets, or at least secure their independence.
For one thing, while Soviet forces under Stalin did not take Lvow until the end of August, they were still capable of tying up Polish forces in the region. More important, perhaps, was disunity in the ranks of Poland’s government. The Polish National Democrats had withdrawn to Posen under the leadership of Roman Dmowski, who spent his time predicting the imminent fall of Warsaw and urging the formation of a separatist regime. The Polish army in Posen was commanded by General Dowbor-Musnicki, an enemy of General Pilsdski. When Warsaw’s government fell, it was forced to flee to the western Polish province, and appointed General Dowbor-Musnicki as the head of the Polish army. This was of course refused by Pilsudski, whose troops ignored its orders. Thus Poland’s military forces were divided and incapable of coordinating, dooming their efforts to resist the Soviets.
And, of course, there are those within Germany who would welcome a separatist Polish regime….
[1] Estonia’s independence was recognized by the USSR in February 1920, And Finland and the USSR were already negotiating a peace by this point.